关键词: 青藏高原, 横向非均匀性, 谱结构, 散射, S波

Abstract: In this paper we present results of spectral structure of crustal velocity inhomogeneity beneath the southeastern margin of Tibetan plateau and its adjacent region based on the S wave envelope broadening algorithm. The spectral structure of 8~16Hz band is selected to analyze the special character of crustal inhomogeneity and discuss the correlation between strong earthquakes and inhomogeneities. The result shows that strong and complex inhomogeneities of crustal medium are found in the southeastern margin of Tibetan plateau and its adjacent region. In the upper part of upper crust, the strong and small scale inhomogeneities are imaged in the Longmengshan fault zone and the north of the Anninghe fault zone, the weak and large scale inhomogeneites are imaged in the section from Huolu to Daofu of Xianshuihe fault zone and the south of the Anninghe fault zone. In the lower part of upper crust, strong inhomogeneites are found in the Longmengshan fault zone, Lianfeng fault zone, the north of the Anninghe fault zone and the sections from Huolu to Daofu of the Xianshuihe fault zone, weak inhomogeneites are found in the section from Daofu to Kangding of Xianshuihe fault zone. In the middle crust, strong inhomogeneities are observed in the section of the Baoxing to Dujiangyan, the Baoxing to Kangding, and Kangding to Shimian, and weak inhomogeneities are observed in the northwestern section from Huolu to Kangding, and the Lianfeng fault zone. Comparing the medium inhomogeneities with the location of the strong earthquakes, our results suggest existence of high correlation between them. Strong earthquakes are often located in the transitionary zone between the strong and the weak inhomogeneities. The spatial distribution of the strong and the weak medium inhomogeneities may be related to the broken medium from the strong movement of geological tectonic and the heat flow upwelling along active faults induced by frequent tectonic and volcanic activity.

Key words: Tibetan plateau, lateral heterogeneity, spectral structure of velocity, seismic scattering, S wave